I’m gonna chime in late here, as someone who has nearly as long a relationship with VampChron/AR as Bryan does: I don’t think this will damage the Hannibal fandom at all, because that Venn diagram overlap pre-dates Bryan Fuller altogether.
Let’s be real: VampChron is a peak 90s fandom, not least due to AR’s own chilling actions afterward, and because there hasn’t been an adaptation of the series since the Queen of the Damned movie in 2001. Anyone who is still excited by this news in a fannish context now, was into it either before or while AR went ham on fanworks (which is why you’re seeing so much anxiety about it - there are Fannibals who have seen some shit directly). And there is going to be almost no one who is actively in Hannibal fandom today, jumping up and down about a new VampChron TV series, who didn’t get into Hannibal in the first place because they were into the Harris novels/movies in the 90s and early 00s.
(Except me. XD; I’m the outlier, though I did watch SotL. And yeah, I’m kinda inviting ppl here to @ me along the lines of “I’m a Millennial who got into both on my own in 2009 bc I live under a rock,” but I think that doesn’t disprove my larger point.)
In short, this is a classic case of “Holy shit, two cakes!” For people who care at all, it was Two Cakes in the 90s, and it’s Two Cakes today, and the only angst is around whether AR will blow her top at crossover fic.